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ISTA Master's Thesis
No full textThe internal dynamical properties of red giant stars have been explored extensively in recent
years as a result of the increase in high precision data availability from the space missions
Kepler and TESS (Transiting Exoplanet Survey Satellite), and in this exploration, it has been
discovered that some of these stars are not behaving as expected. Red giants are stars that have
evolved off of the main sequence after having completed fusing hydrogen into helium in their
core. Observational data shows that the cores are rotating significantly slower than models can
recreate consistently across evolutionary stages. This discrepancy has prompted investigation
into the efficiency of angular momentum transport mechanisms and mixing processes including
meridional circulation, shear instability, internal gravity waves, Tayler-Spruit dynamo, fossil
magnetic fields etc., to explain this behavior.
Analyzing seismic oscillations in stars, via asteroseismology, is a powerful tool as it is the only
way in which the deep stellar interior can be probed and subsequently characterized; this is
possible as global oscillations modulating the stellar surface are effected by internal processes.
For red giants, p-modes (pressure modes; resonating through the entire star) and g-modes
(gravity-modes; resonating in the radiative interior) couple to create mixed modes. These
mixed modes give access to the otherwise hidden stellar interior as g-modes couple to p-modes,
delivering information from the interior to the surface.
Internal magnetic signatures have been observationally confirmed in red giant stars via
asteroseismology and characterized in two ways. One being that dipole mixed modes with
ℓ = 1 will display a global asymmetric frequency shift of its azimuthal components; where
the m = 0 and m = ±1 components of the ℓ = 1 dipole mode will be shifted by two
different power laws, respectively. And the other being a reduced visibility of dipole mixed
mode amplitudes in the power spectra, where stars presenting with this feature are denoted as
suppressed.
Several studies of the suppressed dipole mixed mode amplitudes have been carried out, but thus
far, no dedicated studies of the asymmetric frequency shifts of suppressed red giants have been
conducted; one reason being that the asymmetric frequency shifts cannot be characterized
when the dipole mixed mode amplitudes are severely reduced in many of the suppressed stars.
Sincefullysuppressedstarsdonothavedetectablemixed-modestoevaluate, partiallysuppressed
stars, that is, red giant stars presenting with suppressed dipole mixed modes in select parts of
their power spectra rather than across the entire spectra, will be the subject of this study as
the respective mode amplitudes are still visible at high frequencies.
As such, this study will search for asymmetric frequency shifts on the dipole mixed
modes of partially suppressed red giant stars; the aim here is to investigate if both
mode suppression and magnetic shifting of dipole mixed modes occur simultaneously.
Thisstudywillbeconductedbycreatingapipelinetoestimatepriorsofasteroseismicparameters,
use the priors to model the power spectra with the stellar modeling code sloscillations_ISTA,
and perform a Bayesian fit of the parameters with the simulated data on the star KIC 6975038,
a target with partially suppressed dipolar mode amplitudes identified in the literature, to fit its
magnetic parameters. I present a novel method to model the stellar power spectra of
partially suppressed red giants by application of a sigmoid profile to the ℓ= 1 dipolar
mode component of the spectra. With the results of this study I aim at constraining
the cause of this partial dipole mode amplitude suppression, allowing for more detailed
studies regarding their astrophysical nature. Furthermore, the long term hope for the method
used in this study will be to expand the sample of partially suppressed red giants and fit their
asteroseismic parameters accordingly
LNCS
No full textMarkov decision processes (MDPs) are a fundamental model of decision making which exhibit non-deterministic choice as well as probabilistic uncertainty. Traditionally, verification assumes exact knowledge of the probabilities that govern the behaviour of an MDP. However, this assumption often is unrealistic, e.g. when modelling cyber-physical systems or biological processes. There, we can employ statistical model checking (SMC) to obtain an estimate of the MDP’s value (e.g. the maximal probability of reaching a goal state) that is close to the true value with high confidence (probably approximately correct). Model-based SMC algorithms sample the MDP and build a model of it by estimating all transition probabilities, essentially for every transition answering the question: “What are the odds?” However, so far the statistical methods employed by state-of-the-art SMC verification algorithms are quite naive or even compromise the correctness guarantees.
Our first contribution is to survey, categorize, and analyse statistical methods, identifying those few that are most efficient and that provide suitable guarantees for the verification setting. Secondly, we propose improvements that exploit structural knowledge of the MDP. Both contributions generalize to many types of problem statements as they are largely independent of the setting. Moreover, our experimental evaluation shows that they lead to significant gains, reducing the number of samples that an SMC algorithm has to collect by up to two orders of magnitude
Deleterious mutations and selection for sex in spatially structured, diploid populations
No full textGenetic drift is potentially an important component of selection for sex, as it is a source of statistical associations between alleles at selected loci. By increasing local drift, population structure may thus amplify the evolutionary advantage of sex. However, most previous models have focused either on haploid populations or on diploid populations without spatial structure. In this article, we use two- and three-locus analytical models and multilocus simulations to explore selection for sex in a diploid population structured according to the island model, in the presence of recurrent deleterious mutations. Our results show that selection generally favors an intermediate rate of sex that decreases as the direct cost of sex increases and increases moderately as the degree of population structure increases. Selection for sex is generated by multiple effects involving genetic associations within and between loci. When selection occurs at many loci, it is generally dominated by interference effects involving deleterious alleles at different loci, captured by our three-locus model. In our multilocus simulations, we observed an irreversible spread of asexual mutants under strong costs of sex, and when deleterious mutations are partially recessive. However, population structure may prevent this spread of asexual mutants when dispersal rates are sufficiently small
DebDaB: A database of supraglacial debris thickness and physical properties
No full textDebdaB is a database of measured and reported physical properties and thickness of supraglacial debris that is openly available and open to community submissions.
The majority of the database (90%) is compiled from 172 sources in the literature, and the remaining 10% has not been published before. DebDaB contains 8,286 data entries for supraglacial debris thickness, of which 1,852 entries also include sub-debris ablation rates, 167 data entries of thermal conductivity of debris, 157 of aerodynamic surface roughness length, 77 of debris albedo, 56 of debris emissivity and 37 of debris porosity. The data are distributed over 83 glaciers in 13 regions in the Global Terrestrial Network for Glaciers
Sumset growth in progression-free sets
No full textWe study the growth of sumsets A+B⊂S⊂G, where S does not contain an arithmetic progression of length 2k+1, and where G is a commutative group, in which every nonzero element has an order of at least 2k+1. More specifically, we show the following: if A,B⊂G are sets such that A+B does not contain an arithmetic progression of length 2k+1, then
|A+B|≥|A|2k−13k−2|B|k3k−2.
As an application we derive upper bounds on the cardinality of the summands in sumsets A+B+C contained in the set of t-th powers, where t≥2 is an integer. In particular, we show that min(|A|,|B|,|C|)≪(logN)4/5 for t=2, and min(|A|,|B|,|C|)≪t(logN)1/2 for t≥3
The second Hintereisferner experiment (HEFEX II): Initial insights into boundary layer structure and surface–atmosphere exchange processes from intensive observations at a valley glacier
No full textMountain glaciers offer opportunities to observe boundary layer exchanges in conditions characterized by predominantly stable stratification, thermally driven winds, and varying surface roughness. Logistical challenges involved in instrumenting glacier surfaces mean that in situ observations remain relatively scarce, limiting the use of this outdoor laboratory. The second Hintereisferner Experiment (HEFEX II) was carried out on an Austrian Alpine glacier during summer 2023. This collaborative endeavor, involving 12 institutions from Austria, France, Germany, Switzerland, and the United Kingdom, represents an unprecedented set of observations of glacier microclimate. Instrumentation on the glacier surface consisted of eight 3-m and two 5-m weather stations equipped with multilevel eddy covariance systems and auxiliary instrumentation, and eight additional lower-specification weather stations. These operated successfully for 26 days with minimal data gaps. During a 3-day intensive observational period, additional instrumentation was deployed: a short-path ultrasonic anemometer installed very close to the glacier surface; a high-speed thermal camera capturing high-resolution boundary layer heat transport at the glacier centerline on a synthetic screen; 3D sampling of the glacier boundary layer using two meteorological UAVs; and a Streamline XR Doppler lidar capturing the structure of the above-valley atmosphere. These novel datasets are valuable for improving understanding of glacier–atmosphere exchange processes, the role of glaciers in valley circulation, and how both might be affected by continued climate change and glacier recession. Here, we detail the scientific goals and implementation of the campaign, describe the general weather conditions, and present first insights into what the observations reveal about the glacier boundary layer features observed during the campaign
Rapid optimal work extraction from a quantum-dot information engine
No full textThe conversion of thermal energy into work is usually more efficient in the slow-driving regime, where the power output is vanishingly small. Efficient work extraction for fast-driving protocols remains an outstanding challenge at the nanoscale, where fluctuations play a significant role. In this Letter, we use a quantum-dot Szilard engine to extract work from thermal fluctuations with maximum efficiency over two decades of driving speed. We design and implement a family of optimized protocols ranging from the slow- to the fast-driving regime, and we measure the engine's efficiency as well as the mean and variance of its power output in each case. These optimized protocols exhibit significant improvements in power and efficiency compared to the naive approach. Our results also show that, when optimizing for efficiency, boosting the power output of a Szilard engine inevitably comes at the cost of increased power fluctuations
PMLR
No full textModern deep neural networks exhibit heterogeneity across numerous layers of various types such as residuals, multi-head attention, etc., due to varying structures (dimensions, activation functions, etc.), distinct representation characteristics, which impact predictions. We develop a general layer-wise quantization framework with tight variance and code-length bounds, adapting to the heterogeneities over the course of training. We then apply a new layer-wise quantization technique within distributed variational inequalities (VIs), proposing a novel Quantized Optimistic Dual Averaging (QODA) algorithm with adaptive learning rates, which achieves competitive convergence rates for monotone VIs. We empirically show that QODA achieves up to a 150% speedup over the baselines in end-to-end training time for training Wasserstein GAN on 12+GPUs
Myosin II regulates cellular thermo-adaptability and the efficiency of immune responses
No full textEffective immune responses rely on the efficient migration of leukocytes. Yet, how temperature regulates migration dynamics at the single-cell level has remained poorly understood. Using zebrafish embryos and mouse tissue explants, we found that temperature positively regulates leukocyte migration speed, exploration, and arrival frequencies to wounds and lymph vessels. Complementary 2D and 3D cultures revealed that this thermokinetic control of cell migration is conserved across immune cell types, independently of the 3D tissue environment. By applying precise (sub-)cellular temperature modulation, we identified a rapid and reversible thermo-response that depends on myosin II activity. Small physiological increases in temperature (1°C –2°C), as present during fever-like conditions, profoundly increased immune responses by accelerating arrival times at lymphatic vessels and tissue wounds. These findings identify myosin-II-dependent actomyosin contractility as a critical mechanical structure regulating single-cell thermo-adaptability, with physiological implications for tuning the speed of immune responses in vivo
Is a 1D perturbative method sufficient for asteroseismic modelling of β Cephei pulsators?
No full textSupplementary material for Mombarg et al. (2025, A&A). Title: "Is a 1D perturbative method sufficient for asteroseismic modelling of
~Cephei pulsators? Implications for measurements of rotation and internal magnetic fields"
Content:
- Non-rotating ESTER models and associated .GSM models. (Xini = 0.71, Zini = 0.014, vertical/horizonal viscosity 10^7 cm^2/s, vertical chemical diffusion 10^4 cm^2/s for evolution model. More details on the ESTER models can be found in the ESTER manual.
- Rotational asymmetries computed with StORM and TOP in 1/d, and the central m=0 frequency from TOP in 1/d. (all_A*_new.pkl)
- Magnetic asymmetries in 1/d for different obliquity angles between 0 and 90 deg for ZAMS and MAMS model, for B_0 = 75 kG. *_nu key gives unperturbed mode frequencies, *_npg the radial order (asym_dict.pkl, asym_dict_evol.pkl